Regulation of the human oxytocin receptor by nuclear factor-κB and CCAAT/enhancer-binding protein-β

Context: Increased myometrial sensitivity to oxytocin at term is mediated through increased oxytocin receptor (OTR) expression. OTR promoter contains putative transcription factor-binding sites for activating protein-1 (AP-1), CCAAT/enhancer-binding protein (C/EBP), and nuclear factor-kappa B (NF-kappa B), which may be activated by IL-1 beta, whose concentrations increase with labor. Objective: The objective of this study was to examine the effect of IL-1 beta on OTR expression and the roles of AP-1, C/EBP, and NF-kappa B in OTR promoter function. Results: IL-1 beta induces an increase in OTR mRNA concentrations and OTR ligand binding in myometrial cells, which is maximal at 4 h and decreased after 20 h. IL-1 beta activates the transcription factors AP-1 C/EBP beta, and NF-kappa B. Using computer-based analysis and EMSA studies, we have identified three AP-1, nine C/EBP, and three NF-kappa B DNA-binding sites in the OTR promoter. In transient transfection studies, OTR promoter activity was increased by C/EBP beta and NF-kappa B, but not by AP-1. C/EBP beta and NF-kappa B together had a synergistic action in the induction of OTR promoter activity. Site-directed mutagenesis of each individual C/EBP and NF-kappa B site had no effect on the ability of C/EBP beta, NF-kappa B, or their combination to activate OTR promoter. However, mutation of both NF-kappa B sites inhibited promoter activation by NF-kappa B alone, but not that by the combination of C/EBP beta and NF-kappa B. Deletion studies showed that a region between -851 and -656 of the OTR confers responsiveness to the combination of C/EBP beta and NF-kappa B. Conclusion: IL-1 beta has a biphasic effect on OTR expression in myometrial cells, and C/EBP and NF-kappa B play synergistic roles in OTR promoter activation.